KR101043572B1 - Distribution Automation System and its voltage control method for reactive power compensation - Google Patents

Abstract

The present invention relates to a new power distribution automation system and a voltage control method thereof, which can stably supply voltage to a user by appropriately changing a setting of a voltage controller so that an invalid voltage at each load stage can be compensated. A first step of modeling a distribution system in the form of a distributed load by applying constants of four terminals according to the connection form of each node and a distribution line constituting the control unit; A second step of determining a formula for estimating a voltage magnitude at a corresponding node from a current value of an adjacent node; A third step of determining an objective function including a voltage magnitude value calculated through the equation determined in the second step and a control variable for controlling the same; And a fourth step of calculating a value of the control variable such that the determined objective function has a minimum value and applying the calculated value to each voltage control device at the center of the distribution system.

Distribution system, power current, voltage control, distribution automation system

Description

 Distribution Automation System and its voltage control method for reactive power compensation

The present invention relates to a distribution automation system for reactive power compensation and a voltage control method thereof, and more particularly, a distribution for minimizing power loss by compensating reactive power at each node included in a complex radial distribution system. It relates to an automation system and a voltage control method thereof.

Voltage control in the distribution system should be able to reduce the loss of reactive power by continually providing the consumer with adequately sized voltages without distortion in designing the distribution system.

In addition, as the power demand changes from time to time, the bus voltage supplied to the distribution line is variable, and thus the magnitude of the bus voltage may exceed the appropriate level of the load stage to which the power demand is connected.

Therefore, in order to keep the voltage profile at each load stage connected to the distribution line within an appropriate limit, and to minimize power and energy loss, the control setting in such a voltage controller must be appropriately modified.

Conventionally, methods based on mathematical optimization algorithms such as linear, nonlinear, quadratic programming, Newton and interior methods have been proposed as methods for optimizing voltage and reactive power in a power system.

In addition, fuzzy theory-based methods and expert system methods are used to control voltages in distribution systems, and probabilistic load flow diagnosis methods based on voltage and reactive power control algorithms are also included. In some cases. In addition, a standardized weighting method has been proposed that considers key factors required for voltage control such as reactive power, feeder loss, voltage drop, and voltage profile.

On the other hand, as IT, communication technology, etc. are rapidly developed, a distribution automation system capable of determining abnormality by acquiring voltage and current state data of each load stage of a distribution line even in remote locations is applied to the distribution system. Therefore, a voltage control algorithm for reactive power compensation based on a distribution automation system is required.

According to the present invention, in the distribution automation system, the actual magnitude of the voltage at each load stage can be estimated more accurately than before, and the reactive power is compensated for the estimated calculated voltage to minimize the power loss and stably supply the voltage to the consumer. A new power distribution automation system and voltage control method thereof are proposed.

More specifically, the voltage control method of the power distribution automation system according to an embodiment of the present invention, by applying the constants of four terminals (constants of four terminals) according to the connection form of each node and the distribution line constituting the distribution system A first step of modeling the distribution system in the form of a load; A second step of determining a formula for estimating a voltage magnitude at a corresponding node from a current value of an adjacent node; A third step of determining an objective function including a voltage magnitude value calculated through the equation determined in the second step and a control variable for controlling the same; And a fourth step of calculating a value of the control variable such that the determined objective function has a minimum value and applying the calculated value to each voltage control device at the center of the distribution system.

In addition, a distribution automation system according to an embodiment of the present invention, the voltage control device for providing a voltage of a predetermined magnitude to a node connected in the distribution system according to the control value; A Feeder Remote Terminal Unit (FRTU) connected to each node to measure the magnitude and phase angle of the voltage and current at the node; And a distribution automation server that estimates and calculates the magnitude of the voltage at each node based on the measurement data at each node received from the FRTU, and controls the voltage controller to compensate the reactive voltage for the estimated calculated voltage. do.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

1 is a block diagram showing the configuration of a distribution automation system according to an embodiment of the present invention.

The distribution automation system 1 is connected to each other through a communication network of switchboards distributed in a long distance to transmit system operation information such as voltage or current to the distribution automation server 5 and the data received from the distribution automation server 5. It is a system that operates by monitoring and controlling the status of distribution system through. At this time, each distribution line switch is equipped with a distribution automation terminal (FRTU; Feeder Remote Terminal Unit (FRTU) hereinafter) (F), respectively, wherein the FRTU (F) is each FRTU (F) or voltage control device in the distribution automation server Measurement and transmission of various data necessary to control the operation of the data, such as the magnitude and phase angle of the voltage and current at the node to which the FRTU (F) is connected.

In addition, the distribution system may include various devices for controlling voltage and reactive power. For example, an automatic voltage regulator (AVR) may be provided to control the second bus voltage of the main transformer in the substation on the distribution line according to the operation of the ULTC transformer 10, and a shunt capacitor Condenser 20 may be installed along the feeder of the distribution system to adjust the reactive power of the distribution line. In this case, the SVR (Step Voltage Regulator) 30, which is a type of AVR, may have a difference of about 5% from the maximum rated voltage level in the distribution system.

In the distribution automation system 1 according to an embodiment of the present invention, the control method for the voltage control device may be performed based on data received from each FRTU (F) connected to the distribution system.

In general, the FRTU (F) measures the phase angle of the voltage, the magnitude of the current, or the phase angle of the current to a value almost equal to the actual value, and is transmitted to the distribution automation server 5. However, to measure the magnitude of the voltage, the magnitude of the voltage measured at the node and FRTU (F) at that node, including many errors due to various factors such as load variation, is approximately 20%. Has an error. For example, in detail, the voltage at any node of a distribution system can be measured by connecting a grounding potential transmitter (GPT) to that node. At this time, the measured voltage magnitude has a large value. On the contrary, since the GPT facility has to be directly connected to the distribution line, there is a proposal for the magnitude. Therefore, the transformer ratio in the GPT becomes large, and thus the measurement error becomes large due to the influence of the coil for the transformer.

Therefore, the power distribution automation system according to an embodiment of the present invention proposes an algorithm for estimating the voltage magnitude at each node relatively accurately. In addition, it is possible to adjust the control set value of the voltage control device connected in the system to reduce the voltage drop by compensating the reactive power at each node based on the voltage magnitude value estimated at each node.

In this case, data transmitted and received from each node may be synchronized based on a GPS time value, and a detailed description thereof will be omitted herein.

In the power distribution automation system 1 according to an embodiment of the present invention, the proposed algorithm applies new load modeling.

That is, it is assumed that the load is distributed evenly along the distribution line in the distribution system. The actual load is irregularly distributed throughout the distribution line. Unlike the conventional method which assumes that the loads are irregularly distributed in one section and are concentrated at the measurement point, the present invention uses the 4-terminal integer method. As a method, we gather the irregular loads in each section into one and model the load assuming that the loads are uniformly distributed on the tracks in the sections.

The load information is very important when calculating the load flow that supplies the active power and reactive power required by the load through various types of power supply and line network. Especially, the load information is different in the distribution line with different distribution system. This is even more the case when a complex radial distribution system is distributed. The power dissipated at the load varies with the voltage level, so the load affects the magnitude of the voltage. Accordingly, the proposed algorithm estimates the voltage magnitude at each node by applying a distributed load model different from the conventional method as described above, and a detailed description thereof will be described later with reference to FIG. 3.

In a complex radial distribution system, it is very difficult to obtain a solution for calculating the power flow at each node. The 4-terminal integer method is applied to simplify the load flow calculation process. Since the current data measured in FRTU is almost the same as the actual value, the distribution system modeled by the measured current value and the distribution load is applied to the 4-terminal integer method. Voltage and phase can be calculated.

The coefficient matrix in Equation 1 represents a basic form of the four-terminal forward order method.

At this time, since the different nodes constituting the radial distribution system have different environmental requirements such as connection type, the coefficient matrix for the 4-terminal integer method can be extended as follows in each case.

FIG. 2 is a diagram illustrating various connection types at each node in a distribution automation system according to an embodiment of the present invention, and FIG. 2 (a) illustrates a case of current flowing out from one node. 2 (b) is a diagram showing a current flow at a node including a lead wire, and FIG. 2 (c) is a diagram showing a current flow at a node to which a transformer is connected.

In Fig. 2 (a), Iq is the current flowing into node q and Iqq is the current flowing out of the system. Therefore, the current transferred from the node q to the node r is Iq-Iqq, and the coefficient matrix of the 4-terminal integer from the formula for the voltage and current at the node q is expressed by Equation 2 below.

In the power distribution system, as shown in FIG. 2 (b), a node including branch lines in different directions may appear. At this time, Ip is the load current coming from the node p, IpA is the load current in the interval between the node p and node q. IpB is the load current in the interval between node p and node r, which is the branch of node p, kpq is the current distribution integer in the interval between node p and node q, kpr in the interval between node p and node r Current distribution constant. As shown in FIG. 2 (b), the coefficient matrix of the 4-terminal integer method for voltage and current at node q is expressed by Equation 3 below.

In the case of the node to which the SVR transformer is connected, the equivalent circuit modeling may be represented as shown in FIG. Where z is the impedance of the transformer and the transformer ratio is 1: a. Therefore, the coefficient matrix in the case as shown in FIG. 2 (c) can be derived as shown in Equation (4).

In other words, the four-terminal integer method can be derived by applying all three cases to the complex radial distribution system.

Meanwhile, in the distribution automation system and the voltage control method thereof according to an embodiment of the present invention, a method for estimating a voltage profile in a distribution system includes measuring values measured at a feeder head or another node and feeder parameter values. Can be obtained and used.

3 is a diagram illustrating load distribution between adjacent nodes in a distribution automation system according to an embodiment of the present invention.

The distribution automation system may be composed of five nodes, each of which is provided with a FRTU as shown in FIG. The method of obtaining the voltage profile at each node is to apply the magnitude and phase angle of the voltage and current at node 0 to the proposed algorithm described below so that the magnitude and phase angle data of the voltage and current at node 1 can be calculated. do. Next, the magnitude and phase angle data of voltage and current at node 2 can be calculated based on the value at node 1, and the magnitude and phase angle data of voltage and current at each node can be obtained by repeating the same process in turn. Can be.

The step of calculating the magnitude and phase angle data of the voltage and current at the node 1 through the data measured at the node 0 may be performed as follows.

In order to calculate the magnitude and phase angle data of the voltage and current of node q in the interval between any node p and node q, the line impedance and load admittance y _k between node p and node q are shown in FIG. As shown in the drawing, it is assumed that the distribution lines are evenly distributed every dx. In this case, the basic equations of the voltage drop and the current drop in each load stage may be illustrated as Equation 5 below.

Where zdx is the line impedance per unit length and ydx is the load admittance per unit length.

By calculating the differential equation illustrated in Equation 5, a solution may be derived as in Equation 6.

는 배전 선로의 특성 상수이다.At this time,

Is the characteristic constant of the distribution line.

In Equation 6, the boundary condition of the p side of the node (the current flowing through the node is the sum of the outgoing current and the loss) can be expressed in detail as shown in Equation 7.

In Equation (7), it is assumed that L _k is the length of one section, and when the phase of the voltage and current x = L _k on the load side, Equation (7) may be derived as in Equation (8). In addition, if the voltage and current data at the node p is substituted into the above-described equation, the values of variables other than the load admittance y _k may be calculated.

이다.At this time,

to be.

In Equation 8, _if the value of y _k can be obtained and substituted, Vq can be easily calculated and can be estimated to be almost the same value as the voltage at the actual node q in that there is no error factor in conventional voltage measurement. have.

Therefore, a process of obtaining information about y _k at the load node and obtaining the value is required. At this time, the magnitude of the current is measured from the FRTU and the phase difference between the voltage and the current is measured from the FRTU, and the value of y _k can be calculated considering that it is equal to the power factor angle.

In addition, since the distribution line can be divided into two types, a line connected to the end of the feeder and a line not connected to the feeder, it is preferable to derive correspondingly in both cases.

In the case of a distribution line connected to the end of the feeder, the current value at the end of the feeder is zero. Therefore, after substituting Iq = 0 in Equation 8, the load admittance can be obtained through the Newton-Raphson method. The Newton-Raphson method is a representative method of finding the root of the equation, and is not limited thereto. Any Newton-Raphson method may be applied as long as it can calculate the load admittance value from the above equation.

In the case of a distribution line that is not connected to the end of the feeder, two equations such as Equation 9 may be derived. When Equation 8 is applied to Equation 9, Equation 10 may be derived. have.

는 노드 q에서의 역률각이다. Where i _q is the current magnitude at node q, the load side node,

Is the power factor angle at node q.

Applying the Newton-Raphson method to Equation 10 in the same way as in the first case, the load admittance y _k can be calculated, and in each case the calculated y _k is the magnitude and phase angle of the voltage and current at the load side node. Substituted in Equation 8 to calculate Vq and Iq.

The voltage magnitude value at each node calculated through the steps as described above may be utilized to control the voltage controller connected to the distribution system in the distribution automation server. The proposed voltage control algorithm is based on the gradient method, so that the voltage of each consumer can fall within the acceptable level range.

In a distribution automation system, the FRTU can collect data from the distribution network, and all control devices spaced apart from each other can be controlled by commands issued such that the voltage magnitude falls within an acceptable range. Thus, as shown in FIG. 3, the tap positions in the ULTC, the SVR (line voltage regulator), and the shunt capacitor can be varied. Among the various voltage control devices that can be connected to the distribution system, the objective function for X is determined in consideration of the above three devices. In this case, X may represent both control variables A and state variables represented by V and I.

Where A is the control variable, V is the node voltage, I is the node current, V _ni is the rated voltage at each node, V _i is the calculated voltage at each node, w _i is the weighting factor in each interval, and n Is the total number of nodes.

In the case of the weighting factor, the voltage control is more important in the section with a large load, so it is included in the equation of the objective function. In addition, voltage control at a node having a large deviation between the constant N, the rated voltage, and the estimated calculated voltage may be more important than other nodes, and thus more objective function for the node may be required.

State variables V and I satisfy the circuit equation. For example, in the power distribution system, the circuit equation for the interval k between the node p and the node q is as shown in Equation 12 below, and adding all the circuit equations in all the sections of the distribution system as F (X), It may appear as in Equation 13.

In this case, when the value of the control variable is changed, the node voltage magnitude, the node current magnitude value, and the like may also vary.

In order to find the minimum value as a method for obtaining a solution from the objective function as described above, the equation (11) must satisfy the following equation (14).

,

,

이며, t는 가속계수(acceleration factor)이며, k= 1, 2, ,,, 이다. At this time,

,

,

T is the acceleration factor and k = 1, 2, ,,,.

로 표시될 수 있으며, 이때

는 다음과 같다.In this case, the gradient of the objective function J (X) is

May be represented as

Is as follows.

로 표시될 수 있는데, 상기

에 관한 식에서 제어변수 a_k에 대한 F(X)를 부분 미분하면 다음과 같다.Also, the gradient vector of the state variable for the control variable

It can be represented as above

In the equation for, the partial derivative of F (X) for the control variable a _k is

이다.At this time,

to be.

Therefore, when the solution is obtained by applying the above-described equation to Equation 14, the control variable value for each voltage control device can be calculated.

4 is an exemplary view showing the configuration of a distribution automation system according to an embodiment of the present invention.

As shown in FIG. 4, the power distribution automation system according to an embodiment of the present invention includes 11 nodes, and the ULTC 10, the SVR 30, and the shunt capacitor 20 are included as voltage control devices. do. In this case, the ULTC 10 is connected to the node 1, the SVR 30 is provided between the node 7 and the node 8. In addition, the shunt condenser 20 may be connected to the node 2 to compensate for reactive power on the line.

Distribution line parameters in the distribution automation system according to an embodiment of the present invention are shown in Table 1. In the distribution automation system, FRTU measures, collects and transmits information such as current magnitude and power factor angle value to the distribution automation server as shown in Table 2.

At this time, the transformer ratio of the transformer 10 is 1: 0.8, the compensation coefficient of the shunt capacitor 20 is 0.03.

On the other hand, the objective function according to the power distribution automation system as shown in Figure 4 may be expressed as shown in Equation 15, wherein the weighting coefficient is set to 1 to apply.

,

이며, a ₁ 는 노드 1에서 ULTC의 제어변수, a ₂ 는 노드 2에서 션트 콘덴서의 제어변수이고, a ₃ 은 노드 7에서 SVR의 제어변수로 설정한다. 각 변수의 초기 값은 a ₁ = 1.0, a ₂ = 1.0, a ₃ = 0.8이며, 본 발명의 일실시예에 따른 방법에 따라 각 노드에서의 전압 크기 값을 추정 산출한 결과 값이 표 3에 개시되어 있다.At this time,

,

A ₁ is a control variable of ULTC at node 1, a ₂ is a control variable of shunt capacitor at node 2, and a ₃ is a control variable of SVR at node 7. The initial value of each variable is a ₁ = 1.0, a ₂ = 1.0, a ₃ = 0.8, and the result of estimating the voltage magnitude value at each node according to the method according to an embodiment of the present invention is shown in Table 3. Is disclosed.

Applying the proposed voltage control method to each node, the control variable values for ULTC, SVR, and shunt capacitors can be adjusted to a ₁ = 1.0394, a ₂ = 0.9742, a ₃ = 1.0764, Table 4 shows the magnitude and phase angle values of the estimated voltage and current at the node.

Referring to the voltage magnitude values at each node in Table 3, the voltage drops at the nodes 8 and 11 appear larger than at the other nodes. Therefore, when the distribution automation server delivers the adjusted control setpoints to the voltage controller connected to the node 8 and the node 11, the reactive power at the node 8 and the node 11 is compensated as shown in Table 4, and the degree of the voltage drop is shown in Table 3. It can be seen that significantly reduced than in the case of.

In particular, in the conventional case of compensating for the voltage drop occurring at the feeder end node such as node 8 and node 11 by increasing the voltage magnitude at the Peter head side (substation lead-out), if the load is not connected due to an accident, While the voltage at the arranged node increases to exceed the rated voltage range, in the embodiment according to the present invention, the operation of at least one voltage control device on the distribution line is controlled to suppress the voltage drop, thereby making it more stable than before. Voltage can be supplied.

As described above, the distribution automation system and the voltage control method for the reactive power compensation according to the present invention have been described with reference to the illustrated drawings, but the voltage control at each node is estimated and calculated relatively accurately, and the voltage control provided to the distribution system therefrom. It is apparent that the technical idea of the present invention to change the control settings of the device to minimize power loss and stably provide voltage to the consumer can be easily applied by those skilled in the art within the scope of protection.

1 is a block diagram showing the configuration of a general distribution automation system,

2 is an exemplary diagram showing various connection forms at each node in a distribution automation system according to an embodiment of the present invention;

3 is a diagram illustrating load distribution between adjacent nodes in a distribution automation system according to an embodiment of the present invention; and

4 is an exemplary view showing the configuration of a distribution automation system according to an embodiment of the present invention.

Claims (6)

A first step of modeling the distribution system in the form of distributed load by applying constants of four terminals according to the connection form of each node and the distribution line constituting the distribution system; A second step of determining a formula for estimating a voltage magnitude at a corresponding node from a current value of an adjacent node; A third step of determining an objective function including a voltage magnitude value calculated through the equation determined in the second step and a control variable for controlling the same; And A fourth step of calculating a value of the control variable such that the determined objective function has a minimum value and applying the calculated value to a voltage control device provided in the distribution system; Voltage control method of a distribution automation system comprising a. The method of claim 1, The second step may include determining a formula for a current at a node according to whether a distribution line is connected to a feeder termination and calculating a load admittance therefrom; And Estimating and calculating the voltage level of the corresponding node by substituting the calculated load admittance into the equation determined in the first step. Voltage control method of a distribution automation system comprising a. The method of claim 2, In the second step, the Newton-Raphson method is applied to calculate the load admittance value voltage control method of a power distribution automation system. A voltage control device for providing a voltage of a predetermined magnitude to a node connected in a distribution system according to a control value; A Feeder Remote Terminal Unit (FRTU) connected to each node to measure the magnitude and phase angle of the voltage and current at the node; And A distribution automation server for estimating the magnitude of the voltage at each node through measurement data at each node received from the FRTU, and controlling the voltage controller to compensate for the reactive voltage for the estimated calculated voltage. Distribution automation system comprising a. The method of claim 4, wherein The voltage control device is at least one or more of Under Load Tap Changer (ULTC), Step Voltage Regulator (SVR), and Shunt Condenser. The method according to claim 4 or 5, The distribution automation server estimates and calculates the magnitude of the voltage at the node based on the magnitude and phase angle measurement data of the current received from the FRTU of the adjacent node, and issues a control command to the voltage controller connected to the node to calculate the estimate. Distribution automation system to ensure that the voltage is within the rated voltage range at the node.

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